Project Summary Molecular and genetic studies using mice show that neural crest-derived cells give rise to the trabecular meshwork as well as the stroma and endothelium of the cornea and are critical for the formation of the anterior segment of the eye. A failure of the normal development of the anterior segment of the eye in humans leads to anomalies in the structure of the mature anterior segment, associated with an increased risk of glaucoma and corneal opacity. The transcription factor Foxc1 is expressed in neural crest- and mesoderm-derived periocular mesenchyme surrounding the developing eye. We have previously shown that heterozygous and homozygous null mutant mice for Foxc1 have numerous ocular abnormalities, including lack of the anterior chamber and corneal endothelium, iris dystrophy and abnormalities of the trabecular meshwork. Mutations in human FOXC1 are associated with autosomal-dominant Axenfeld-Rieger Syndrome (ARS), a disorder characterized by anterior segment defects, glaucoma and other extraocular anomalies. Foxc2, a closely related factor, is expressed in neural crest-derived periocular mesenchyme, and Foxc2 heterozygous and compound Foxc1; Foxc2 heterozygous mutant mice have similar defects such as iris abnormalities to those in Foxc1 heterozygous mutants. However, the exact role of Foxc2/FOXC2 with respect to Foxc1/FOXC1 during anterior segment development is still unknown. Our new data let to the central hypothesis that Foxc1 and Foxc2 have overlapping as well as distinct roles in development of the anterior segment of the eye and corneal avascularity. This hypothesis will be tested by: (1) analyzing the formation of the anterior segment of the eye in a series of neural crest- and mesoderm-specific Foxc mutants as well as Foxc2 knock-in mice, (2) elucidating corneal NV in a series of neural crest- and mesoderm-specific Foxc mutants as well as Foxc2 knock-in mice, and (3) defining the angiogenic properties of Foxc- mutant corneal keratocytes. Successful completion of the proposed experiments will provide valuable insight into the overlapping and unique roles of Foxc1 and Foxc2 in anterior segment development and corneal avascularity and into the fundamental mechanisms that lead to the development of therapeutic strategies designed to inhibit corneal NV.